AB Chase Concert Grand

[Dean May]

Hold on now, Bill. Don't fall asleep just yet.

>>...they don't stand in line between the block and
the hitchpin web, bracing directly against the string load. They do
perform a "tension bracing" in that they prevent the plate struts and
hitchpin webs from buckling upwards...

First you say they don't brace against string load. Then you say they do
prevent struts and webs from buckling upwards. Tell me what is the load that
wants struts and webs to buckle upwards? Is it not the string load?


>>...but it's not the compression bracing provided by the horn.

I don't understand what you mean here. Probably because I am somewhat
ignorant of what the purpose of the horn is. In the context of your post, it
seems the intent of the horn is to push upward on the hitchpin web. Is that
what you are saying?

Del wrote: ... a couple of large wood screws on
each end don't count. Dowels and glue joints do as long as they are still
structurally sound. But many pianos do not have glued-in pinblocks. So then
we have to consider how stress from the strings is supposed to coupled down
through the two ends of the pinblock, across a floppy bellyrail and into the
bellybraces which are supposed to be carrying all this string load.

Stress will be transmitted through the two screws, across the "floppy" belly
rail and to the beams. I have never done a pull test to see how much load
those large screws will hold before they pull out, but I suspect it is
significant, at least 1000 lbs. And I've seen many pianos with screws
through the plate into the rim and belly rail, bypassing the pinblock.

And the floppy belly rail supported by the keybed makes for a pretty
substantial member, it seems to me. I guess it would be easy enough to load
test and measure deflections. (something tells me you've already done this).

I am not arguing that the beams are carrying a significant portion of the
string load, only some, and in that measure they are adding to the rigidity
of the plate.

I guess we could string a plate outside the piano, bring it up to tension,
and see how much deflection we get. (maybe you've already done this too
;-) )



Blessings,

Dean

Dean May             cell 812.239.3359
PianoRebuilders.com   812.235.5272
Terre Haute IN  47802